In present-day missile applications it is important to provide data indicative of rotational motion of a missile as well as position and velocity data to a computer on board the missile for the purpose of calculating adjustments in trajectory to arrive at a desired endpoint. Typically, such systems rely upon multiple gyroscopes, one each for providing an indication of rotational motion along the x (roll), y (pitch), and z (yaw) axes of such missiles to the onboard computer. In addition, accelerometers are provided along the same axes as the gyroscopes for purposes of measuring translational motion along the respective axes with the data from both the gyroscopes and the accelerometers being provided to an onboard computer to adjust the trajectory of the missile, in a conventional manner, based on the data received as compared to a calculated endpoint or set of data to arrive at an endpoint. The real-time inflight data is compared to preset data to adjust the trajectory in flight to arrive at the predetermined target destination. An example of the typical systems to which the invention is directed is disclosed in U.S. Pat. No. 5,067,084, which is commonly assigned herewith, and which disclosure is incorporated by reference herein.
In the past, such a combination of units, i.e., accelerometers and gyroscopes, were known as a core inertial measurement unit. Typically, in order to provide a reference prior to launch for calculations being conducted in flight for measurements during the flight, a referenced set of values is provided along each axis relative to rotational position as well as relative to a base gravitational pull, i.e., gravity at sea level, at the launch site. Such base measurements have in the past been provided by gimbaling the inertial measurement unit about at least two axes. Such an arrangement has required a complicated and expensive gimbaling unit, which is essential to ensure missile targeting accuracy.
The systems with complicated gimbaled inertial measurement units have been in use in both intercontinental ballistic missile application as well as in interceptor missile applications, the latter requiring only a lower level of accuracy over short distances. In the case of applications of the prior art inertial measurement unit on intercontinental ballistic missile systems (ICBMs), accuracy was often enhanced by the use of a conventional star sensor which referenced a predetermined celestial body in flight to provide additional data to the onboard computer which would provide further adjustments to the trajectory of the projectile or missile.
In accordance with the present invention, the requirement of the complicated gimbaling mechanisms of the prior art are avoided. Specifically, it is possible to use a nongimbaled, strapdown base inertial measurement unit (IMU) while maintaining the high accuracy of the prior art systems. The invention provides a system which is much simpler to construct and much less costly than the previous systems.